Key operated lock

ABSTRACT

A key operated lock including a housing having a cylindrical bore therethrough in which a plug is rotatably mounted. Apertures extend radially outwardly in the housing from the bore and each slidably receives a driver. Each driver is aligned, in one position of the lock, with a tumbler assembly movably positioned in an aperture in the plug. The tumbler assembly- receiving apertures communicate with a main key slot in the plug, and insertion of a main key in this slot biases the several tumbler assemblies to a lock-opening position in which the tumbler assemblies contact the drivers along a shear line lying in the interface between the plug and body. The tumbler assemblies are adjustable in their dimensions so that they may be altered to permit a new key to be made operative for opening the lock. Each tumbler assembly includes two relatively movable parts which are interlocked by a locking pin until it is desired to alter the assembly&#39;&#39;s dimension for key changing purposes. The locking pins are cammed to the interlocking positions by cam plates. These cam plates line up with the driver apertures when the plug is rotated to a key changing position, and in this position, a change key can be inserted in a change key slot in the plug to bias each locking pin to a position in which the two relatively movable parts of each tumbler assembly are disengaged. The tumbler assemblies can then automatically accommodate their dimensions to an entirely different main key inserted in the main key slot.

United States Patent {72] Inventor Lewis J. Hill 4121 N.W. 61st Terrace, Oklahoma City, Okla. 73112 [21] Appl. No. 11,668 [22] Filed Feb. 16,1970 [45] Patented June 29, 1971 [54] KEY OPERATED LOCK 14 Claims, 6 Drawing Figs.

[52] US. Cl 70/384, 70/364, 70/378 [51] Int. Cl ..E05b15/14, E05b 27/02 [50] Field of Search 70/364 R, 364 A, 384, 376, 378, 382, 383

[56] References Cited UNITED STATES PATENTS 2,194,469 3/1940 Fremon 70/364 2,232,017 2/1941 Wilder 70/364 3,175,379 3/1965 Russell 70/383 3,320,781 5/1967 Hill 70/384 Primary Examiner-James A. Leppink Assistant Examiner-Robert L. Wolfe ArtorneyDunlap, Laney, Hessin and Dougherty several tumbler assemblies to a lock-opening position in which the tumbler assemblies contact the drivers along a shear line lying in the interface between the plug and body. The tumbler assemblies are adjustable in their dimensions so that they may be altered to permit a new key to be: made operative for open ing the lock. Each tumbler assembly includes two relatively movable parts which are interlocked by a locking pin until it is desired to alter the assemblys dimension for key changing purposes. The locking pins are cammed to the interlocking positions by cam plates. These cam plates line up with the driver apertures when the plug is rotated to a key changing position, and in this position, a change key can be inserted in a change key slot in the plug to bias each locking pin to a position in which the two relatively movable parts of each tumbler assembly are disengaged. The tumbler assemblies can then automatically accommodate their dimensions to an entirely different main key inserted in the main key slot.

lKlEY OPERATED LOCK BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to improved key operated locks. More particularly, but not by way of limitation, this invention relates to an improved key operated lock incorporating mechanism adapted to permit the lock to be easily and rapidly changed for operation by different keys.

2. Brief Description of the Prior Art In my US. Pat. No. 3,320,781, I depict and describe a lock which can be quickly and easily structurally altered so that a different key can be used to operate the lock, and the key previously operable for opening the lock will no longer do so. The value of a structure of this type in which the operative key can quickly and easily be changed is self-evident.

The lock described in my US Pat. No. 3,320,78l includes a body which has a cylindrical bore therein. An elongated plug is rotatably mounted in the bore. A plurality of drivers are positioned in apertures which extend radially through the body into the bore. A plurality of adjustable tumblers are positioned in the plug for radial movement in response .to a main key inserted in the lock. The arrangement and construction of the lock provides for cooperation between the drivers, tumblers, plug and body to prevent relative rotation between the plug and the body when the wrong main key or no main key is inserted in the lock, thus preventing the look from being moved to an open or unlocked position. However, the cooperation between drivers, tumblers, plug and body is such that, when the proper key is inserted, the plug can be rotated to an unlocking position.

The adjustability of the tumblers which are provided in my prior lock construction is the key to the operation of the lock to permit its operativeness with different selected keys to be varied. The tumblers are adjustable in their length (in a radial sense relative to the cylindrical bore) by means of a change key which is inserted in a change key slot in the elongated plug. As this change key is inserted in the change key slot, it biases a latch means used to hold two portions of each tumbler in engaged relationship to a disengaging position so that these two portions of the several tumblers can move freely relative to each other.

When the tumblers are in this status, their lengths are adjustable to operatively conform them to any key which may be inserted in the main key slot. After a new main key of difi erent configuration has been inserted in the main key slot with the two portions of the tumbler disengaged from each other in the manner described, the change key is removed to permit the latch means to move back to its position in which it effects en gagement between the two relatively movable portions of each tumbler. The tumblers are now secured in a fixed length status such that they conform to the configuration of the new main key, rather than the configuration of the key previously used.

Each latch means which is employed for engaging the portions of each tumbler to each other, or for permitting the relative positions of these portions to be adjusted, includes an elongated member which has a portion extending into engagement with the two relatively movable portions of the tumbler, and another part which extends to a position for engagement with the change key when it is inserted in the change key slot. This elongated member is biased to its tumbler locking position by a spring which constantly acts to force it into the position locking the relatively movable parts of the tumbler against relative movement at such time as the bias of the spring is not overcome by insertion of the change key.

In addition to the described structure, my key operated lock as described in my U.S. Pat. No. 3,320,781 further includes a safety plate which retains the change key in its slot, once it has been inserted therein, until a new main key has been inserted in the main key slot.

BRIEF DESCRIPTION OF THE PRESENT INVENTION The present invention constitutes an improved key operated lock which has certain advantages over my previously patented key operated lock by reason of a simplification of structure, which simplified structure is more reliable in opera tion and is characterized in having a longer and more troublefree operating life.

Broadly described, the lock of the present invention comprises a body having a cylindrical bore formed therein, and having an elongated plug rotatably mounted in this bore. A plurality of drivers are positioned in apertures which extend radially in the body and communicate with the bore. At least one adjustable tumbler is positioned in radially extending openings in the plug, with the tumblers being positioned to contact a main key inserted in a main key slot or passageway in the plug. The tumblers and drivers cooperate with each other so that, at a time when the correct main key is inserted in the lock, the plug may be rotated in the body without interference or obstruction by either the drivers or the tumblers, and so that when the improper key is inserted in the lock, one or more tumblers and/or drivers extend across the shear line at which the plug mates with the body so as to prevent rotation of the plug in the body.

The tumblers are each of multipart construction with the parts being movable relative to each other in order to vary the dimension of each tumbler, and it is this adjustability of each tumbler dimension which permits the lock to be accommodated to different keys. Locking pins are provided for interlocking the relatively movable parts of each tumbler so that the dimension of each tumbler can be fixed when the locking pins are in the engaging position. Each of the locking pins includes a projecting portion engageable with a change key when the change key is inserted in a change key slot into which the projecting portion of each locking pin extends when the plug is rotated to a preselectedposition.

Cooperating with the several locking pins are a plurality of cam plates movably mounted in slots formed in the plug. The cam plates bear against the surface of the cylindrical bore formed in the lock body and bias the locking pins into locking engagement with the relatively movable parts of the several tumblers at a time when the plug is not rotated to the change key insertion position. When the cylinder is rotated to the change key insertion position, the cam plates are aligned with the radially movable drivers in the body. In bearing against these movable drivers, the cam plates can be moved outwardly into the driver apertures in the body when the locking pins are moved outwardly by insertion of the change key. With the described disengagement of the locking pins from the relatively movable parts of the several tumblers, the tumblers are automatically self-adjusting to accommodate themselves to a new main key which is inserted in the: main key slot. With the withdrawal of the change key, the locking pins are released, and when the plug is rotated in the body by turning the new main key, the pins are biased inwardly into a position in which the relatively movable parts of the tumblers are interlocked by the locking pins.

From the foregoing description of the invention, it will be perceived that the invention provides an improved key operated lock which includes simple and mechanically strong mechanism and which facilitates the rapid and relatively simple change of the main keys used therein to provide a secure lock which cannot be compromised by the existence of outstanding keys which have previously been adequate for unlocking the lock.

An important object of the invention is to provide a relatively less expensive changeable key operated lock which is yet characterized in having a longer and more trouble-free operating life.

Another object of the invention is to provide an improved changeable key operated lock that can be changed for operation by different keys without the necessity to disassemble the lock.

A further object of the invention is to provide an improved changeable key operated lock that is tamper-proof.

Other objects and advantages of the invention will be apparent from the following detailed description of the invention and from the accompanying drawings which illustrate the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an end elevation view of a key operated lock cnstructed in accordance with the present invention, and showing the lock in its status at the time it is locked.

FIG. 2 is a sectional view taken along line 2-2 of FIG. I with certain parts broken away and certain parts sectioned for greater clarity of illustration.

FIG. 3 is a detail view showing one of the tumbler assemblies and cam plates used in the key operated lock of the invention.

FIG. 4 is a transverse sectional view through the lock at the location of one of the tumbler assemblies in the lock and illustrating the status of the lock at a time that the lock is being accommodated to a new key.

FIG. 5 is a sectional view through a lock similar to the sectional view shown in FIG. I, but illustrating the status of the tumblers and drivers of the lock when an improper main key has been inserted therein.

FIG. 6 is a change key used in the lock of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION In the drawings, the lock of the invention includes a cylindrical body 10 having a cylindrical bore 12 (see FIG. 4) formed axially therein and receiving an elongated, generally cylindrical plug 14. The plug is provided with a main key slot 16 and a change key slot 18 which extend lengthwise in the plug for receiving a main key and a change key as hereinafter described.

In the illustrated embodiment of the invention, the cylindrical body 10 has a plurality of radially extending cylindrical apertures 20 formed through the wall thereof and communicating with the bore 12 (see FIGS. 4 and 5). The radial apertures 20 are closed at their upper ends by a closure plate 22 which is secured in a slot 24 formed longitudinally along the upper side of the body 10. Slidably positioned in each of the apertures 20 is a driver 26. Each driver 26 is preferably of hollow cylindrical configuration so that a spring 28 may be positioned with one end inside the driver, and the other bearing against the plate 22. Each of the drivers 26 is thus biased downwardly in the radial apertures 20 by the respective spring 28.

The elongated plug 14 which is rotatably mounted in the body 10 has secured to one end thereof which projects outside the body, a latch member 30 which, during the operation of the lock, is rotated into engagement with a slot in the doorjamb, or other engaging recess, to lock the door in which the lock is located. The plug 14 is provided with a series of axially aligned, radially extending apertures 32 which communicate with the outer side of the plug, and also communicate through seats 33 (see FIG. 4) with the key slot 16 which extends through the plug. The apertures 32 are positioned in the plug 14 so that when the plug is rotated within the body 10 to one position, such as that shown in FIGS. 2 and 5, the apertures 32 in the plug are aligned with the apertures 20 in the body 10.

Positioned within each of the apertures 32 in the plug 14 is a tumbler mechanism designated generally by reference numeral 34. Each tumbler mechanism is slidable radially within its respective aperture 32, and includes a tumbler cap 36 of hollow cylindrical configuration, a spring 38 positioned within the tumbler cap, a plunger designated generally by reference numeral 40, and a locking pin designated generally by reference numeral 42. It will be noted that the locking pin 42 is of T-shaped configuration and includes a projecting flange portion 434, a barrel 46 and a tip 48 formed on the end of the barrel which is opposite the flange portion 44. The barrel 46 of the locking pin projects through a bore 50 formed in a side arm 52 which projects outwardly from the cap 36.

The plunger 40 is provided with a plurality of spaced, circumferential ribs 54 along its length between which the tip 48 of the locking pin 42 may project when the locking pin is in the position shown in FIG. 3. In this status, the locking pin functions to engage the cap 36 with the plunger 40. It will be noted that the upper end of the plunger 40 contacts one end of the spring 38 which has its other end in contact with the closed upper end of the cap 36. It will also be noted that each plunger 40 has a beveled head 56 which functions to cooperate with the milled tumbler-engaging edge of a main key in a manner hereinafter described.

Each of the apertures 32 formed in the plug 14 opens at one of its sides into asubstantially semicircular slot 60 cut radially inwardly into the side of the plug 14 and of the general configuration shown in FIG. 4. There is one of the semicircular slots 60 cut in the body of the plug 14 in correspondence to each one of the apertures 32, with the series of longitudinally spaced semicircular slots 60 in the plug registering with the se ries of radial apertures 32 formed therein. The series of semicircular slots 60 cut in one side of the plug 14 are intersected by a longitudinally extending slot 62 cut along a major portion of the length of the plug 14 and extending from the outer surface of the plug in a radially inward direction. At its base, the longitudinally extending slot 62 intersects the relatively small change key slot 18 which extends through the plug 14 in a direction parallel to the slot 62 and extends radially inwardly therefrom. This relationship is perhaps best illustrated in FIG. 4 of the drawings where a change key 66 is depicted in position in the change key slot 18, and the lower portion of the longitudinally extending slot 62 is perceptible in full lines and its upper portion in dashed lines.

A cam plate 70 is provided in a cooperating relationship with each of the tumbler assemblies 34. The cam plate 70 has a flat surface 7ll which bears against the flange 44 of the locking pin 42 and has a rounded cam surface 72 on the opposite side of the cam plate from the flat surface 71. A cam plate 70 is provided for contact with each of the locking pins 42, and each cam plate is elongated and relatively thin in configuration as can be seen in referring to these elements in FIGS. 2 and 3.

Each of the cam plates 72 has locating pins 74 projecting from the opposite sides thereof. The cam plates are positioned in the several semicircular slots 60 with the locating pins extending into the longitudinal slot 62 in the plug 14 in the manner best illustrated in FIG. 2. The cam surfaces 72 of the several cam plates '70 will, in most positions of the plug 14 within the housing 110, bear against the cylindrical wall of the bore 12 in the housing 10. However, in one position to which the plug 14 may be rotated, the cam surfaces 72 of the several cam plates 70 are aligned with the apertures 20 in the housing 10 which receive the drivers 26, and this position of the cam plates, upon proper rotation of the plug 14, is depicted in FIG. 4. It will be noted that when the plug I4 is rotated to the position shown in FIG. 4, the cam plates 70 may be moved radially outwardly, as may the locking pins 42 with which these plates are in contact. As will be subsequently explained, this status of the lock permits the change key 66 to be utilized for biasing the locking pins 42 to the disengaging status so that the plunger 40 and cap 36 may move relatively to each other.

OPERATION In describing the operation of the key operated lock of the invention, reference will initially be made to FIGS. 1 and 2. In these two figures of the drawings, the lock is illustrated in a status in which the proper main key which is required for opening the lock has been inserted in the main key slot 16 formed in the plug 14. The latch member 30 behind the plug 14 and body 10 projects from one side thereof so that the lock is now in the locked status. It will be noted in referring to FIG. 2 that the main key 80, in extending into the main key slot 16 in the plug 14, biases the tapered surfaces 56 of the plungers 40 upwardly. The various plungers in the series of tumbler assemblies are at different levels in correspondence to the manner in which the key surface is milled. At this time, the plungers 40 are interlocked with the caps 36 by the location of the locking pins 42 in the position shown in FIG. 3.

As has previously been explained, with the locking pins in their engaging status as here shown, the overall length (in a radial sense) of each tumbler assembly 34 is fixed. It will be seen in referring to FIG. 2 that the tumbler assembly engaging surface of the main key 80 is milled to different depths along its length. It will also be perceived that the overall lengths of the tumbler assemblies 34 which engage the main key 80 as shown in FIG. 2 vary, but that the top surfaces of the caps 36 of the several tumbler assemblies are aligned along the meeting line between the external peripheral surface of the cylindrical plug 14 and the cylindrical body 10. By reason of this status of the caps 36 of the several tumbler assemblies 34, the drivers 26 contained in the radial apertures 20 are also forced upwardly against the bias of their respective springs 28, so that the lower surfaces of the several hollow cylindrical drivers are also aligned along the meeting line between the plug 14 and the body 10. By virtue of this positioning of the drivers 26 and the tumbler assemblies 34, these structural elements do not interfere with rotation of the cylindrical plug 14 within the body 10, since neither the tumbler assemblies nor the drivers project in a radial sense into both the apertures located in the plug 30 and the body.

On occasions when, for security reasons, it is desired to change the mechanism of the lock in such a way that a different main key 30 will fit and unlock the lock rather than one previously in use, the owner of the building in which the lock of the invention is located may effect such change quite quickly and easily. This is accomplished by initially placing one of the old main keys, which previously was effective for operating the lock, in the main key slot 16 so that the tumbler assemblies 34 and drivers 26 are brought to the release position shown in FIG. 2. The main key 80 which has previously been in use is then turned to rotate the plug 14 from the position depicted in FIGS. 1 and 2 to a position 90 therefrom so that the main key slot 16 and the main key 80 then in the position depicted in FIG. 4.

When the cylindrical plug 14 has been rotated to this posi tion, the locking pins 42 and the respective cam plates 70 associated therewith are carried by the plug 14 to the position depicted in FIG. 4. It will be noted that in this position, the cam plates are aligned with the radial bores 20 in which the several driver elements 26 are located, and the cam surfaces 72 of the several cam plates can bias the drivers 26 upwardly within the apertures 20 as has been hereinbefore explained. Moreover, the cam plates 70 are, at this time, free to move up wzrdly relative to the axis of the cylindrical plug 14 so that the locking pins can also move upwardly in following the cam plates. When the lock has been brought to the described status by rotation of the old main key 80, the change key 66 depicted in FIG. 6 is then inserted in the change key slot 18. It will be noted that the change key 66 has a beveled end 66a which permits this end of the change key to pass under, and wedge upwardly, the flange portions 44 of the several locking pins 42 as the change key is inserted in the change key slot 18.

As the change key 66 is moved inwardly in its slot 18 in the plug 14, each locking pin 42 is biased outwardly in a radial direction with respect to the axis of the plug 14, forcing the cam plates 70 outwardly to the positions illustrated in FIG. 4. It will be noted in referring to FIG. 4 that the barrel 46 and tip 48 of each locking pin 74 has been retracted so that it does not engage the respective plunger 40 in the associated tumbler assembly 34 at a location between the spaced circumferential ribs. Stated differently, at this time, each tumbler cap 36 is disengaged from the plunger 40 which is inserted therein so that the plunger is free to move relative to the tumbler cap.

With the locking pins 42 retracted to disengage the plungers 40 from the tumbler caps 36 in each of the tumbler assemblies 34, the old main key is then withdrawn from the lock. The plungers 40 will then, of course, be biased by their respective associated springs 38 to an extended position in which the beveled head 56 rests upon the seat 33 formed at the lower end of the respective apertures 32 and immediately adjacent and contiguous to the main key slot 16.

While the change key 66 is still in position, a new main key which has the tumbler engaging surface milled in a different configuration from the old main key is then inserted in the main key slot 16. The plungers 40 of the several tumbler assemblies 34 are, of course, at this time free to move relative to the tumbler caps 36. Therefore, insertion of the new main key will force the plungers 40 upwardly as the leading end of the key passes, and the plungers will then be forced by their respective springs 38 to a position in which the beveled head of each plunger engages the portion of the milled surface of the key immediately below the respective tumbler assembly 34 in which the plunger is located.

It will be perceived that, at this time, the effective length of each tumbler assembly 34 is the distance from the location of the respective beveled head of each of the plungers 40 to the upper surface of each tumbler cap 36 which, at this time, is located in contact with the inner peripheral surface of the cylindrical bore 12 through the cylindrical body 10. It will further be noted that this location of the top surface of each of the tumbler caps 36 corresponds in a radial sense to the same -location which the top surface of each tumbler cap will need to occupy at a time when the respective tumbler assemblies are in an unlocking status similar to that depicted in FIG. 2. In other words, the overall dimensions of the several tumbler assemblies 34 are, at this time, the same dimensions as those which will be required when the new main key is inserted in the lock for the purpose of unlocking :it.

With the new main key thus positioned, and the several plungers 40 of the respective tumbler assemblies 34 occupying the described relation to the several tumbler caps 36 in these assemblies, the change key 66 is then removed from the change key slot 18. This will permit the several locking pins 42 to slide downwardly in the bores 50 in which they are located so that the tip 48 at the end of the barrel 46 of each locking pin again engages the respective plunger 40 by projection between the spaced circumferential ribs 54. The plungers are now locked in the desired position relative to the tumbler caps 36. The new main key is now rotated so as to rotate the cylindrical plug 14. This motion will cam the several cam plates 70 downwardly to where their rounded cam surfaces 72 may pass freely inside the inner peripheral surface of the cylindrical bore 12 through the cylindrical body 10. The dimensions of the several tumbler assemblies 34 have now been changed so that these assemblies are accommodated to the new main key, and the tumbler assemblies will no longer accommodate the old main key to permit the lock to be unlocked.

At a time when it is desired to unlock the lock, the new main key is inserted to bring the tumbler assemblies 34 into the relationship to the drivers 26 depicted in FIG. 1. The lock may then be unlocked in the manner well understood in the art,

Although a preferred embodiment of the present invention has been herein described in order to provide an example of the construction of the lock of the invention sufficient to enable those skilled in the art to practice the invention, it is to be understood that various changes and modifications may be made in the described and depicted structure without departure from the basic principles which underlie the inventions. Changes and innovations of this type are therefore deemed to be circumscribed by the spirit and scope of the invention except as the same may be necessarily limited by the appended claims or reasonable equivalents thereof.

What I claim is:

1. A lock comprising:

a body having a cylindrical bore therein;

a plug rotatably mounted in the bore and having a main key slot and a change key slot formed therein and extending in a longitudinal direction with respect to said cylindrical bore;

drivers movably mounted in the body for radial movement relative to the bore, and for movement partially into the bore;

tumbler assemblies movably mounted in the plug for radial movement relative to the bore and movable to a position projecting from the plug, the tumbler assemblies and drivers contacting each other in one position of said plug in relation to said body, each of said tumbler assemblies comprising:

a cap positioned for contacting one of said drivers when said plug is in said one position;

a plunger movably mounted relative to said cap for adjusting the length of the tumbler assembly, and having a portion projecting into said main key slot;

a locking pin engaging said plunger with said cap to prevent relative movement therebetween and to selectively fix the length of the tumbler assembly, a portion of said locking pin projecting into said change key slot; and

cam plates each contacting one of said locking pins and each movably mounted in a slot in said plug and having a cam surface projecting into contact with the wall of the bore in said body, said cam plates each having said cam surface positioned for contacting one of said drivers to permit radial displacement of said locking pins and cam plates when said plug is rotated to a second position relative to said body.

2. A lock as defined in claim 1 wherein each of said locking pins is T-shaped in configuration and includes:

a barrel extending slidably through said cap;

a tip on the end of said barrel and engageable with said plunger in one position of the locking pin; and

a flange portion contacting one of said cam plates and spaced from said cap to permit a change key to be passed between said flange portion and said cap.

3. A lock as defined in claim 1 wherein said plug is further characterized in having a plurality of longitudinally spaced, substantially semicircular slots extending radially inwardly therein from the outer peripheral surface thereof, and having a longitudinally extending slot extending radially therein from the outer periphery thereof and intersecting said semicircular slots at substantially a right angle, each of said semicircular slots receiving one of said cam plates.

4. A lock as defined in claim 2 and further characterized to include locating pins extending from opposite sides of each of said plates into said longitudinally extending slot.

5. A lock as defined in claim 1 and further characterized as including a spring contacting each of said drivers and located radially outwardly thereof for biasing said driver radially inwardly in said body toward said cylindrical bore.

6. A lock as defined in claim 1 and further characterized as including a spring positioned between each of said caps and the associated plunger in each of said tumbler assemblies for biasing each plunger toward said main key slot, and each of said caps radially outwardly relative to said cylindrical bore.

7. A lock as defined in claim 1 wherein each of said plungers has a plurality of circumferential ribs spaced from each other therealong and selectively engageable by one of said locking pins.

8. A lock as defined in claim 1 wherein each of said caps is generally cylindrical in configuration and receives a portion of the associated plunger therein, each cap further having a bored side arm projecting from one side thereof and slidingly receiving a portion of one of said locking pins.

9. A lock as defined in claim 8 wherein each of said locking pins is T-shaped in configuration and includes:

a barrel extending slidably through the bored side arm of the cap associated therewith; a tip on the end of said barrel and engageable with the portion of the plunger in said cap; and a flange portion contacting the outer end of said side arm and contacting one of said cam plates, said flange portion being spaced from the cap associated therewith to permit a change key to be passed between said flange portion and said cap.

10. A lock as defined in claim 9 wherein said plug is further characterized in having a plurality of longitudinally spaced, substantially semicircular slots extending radially inwardly therein from the outer peripheral surface thereof, and in having a longitudinally extending slot extending radially therein from the outer periphery thereof and intersecting said semicircular slots at substantially a right angle, each of said semicircular slots receiving one of said cam plates.

II. A lock as defined in claim 10 and further characterized to include locating pins extending from opposite sides of each of said cam plates into said longitudinally extending slot.

12. A lock as defined in claim 11 and further characterized to include springs contacting each of said drivers and located radially outwardly thereof for biasing each driver radially inwardly in said body toward said cylindrical bore.

13. A lock as defined in claim 1 and further characterized as including a spring positioned between each of said caps and the associated plunger in each of said tumbler assemblies for biasing each plunger toward said main key slot and each of said caps radially outwardly relative to said cylindrical bore.

14. A lock comprising:

a body having a cylindrical bore therein;

a cylindrical plug rotatably mounted in the bore and having a main key slot and a change key slot formed therein;

drivers movably mounted in the body for radial movement relative to the bore and for movement partially into the bore;

tumbler assemblies movably mounted in the plug for radial movement relative to the bore and movable to a position projecting from the plug, the tumbler assemblies and drivers contacting each other in one position of said plug in relation to said body, each of said tumbler assemblies comprising:

a first part positioned for contacting one of the drivers when said plug is in said one position;

a second part movably mounted relative to said first part for adjusting the overall length of the tumbler assembly, and having a portion projecting into said main key slot for cooperation with a main key inserted therein;

a locking pin engaging said second part with said first part to prevent relative movement therebetween and to selectively fix the length of the tumbler assembly, a portion of said locking pin projecting into said change key slot for cooperation with a change key; and

cam means contacting each of said locking pins and each movably mounted in said plug, each of said cam means having a portion projecting into contact with the wall of the bore in said body and aligned with said drivers for contacting said drivers to permit radial displacement of the drivers in the body, and a following movement by the cam means to permit radial displacement of said locking pins and cam plates when said plug is rotated to a second position relative to said body. 

1. A lock comprising: a body having a cylindrical bore therein; a plug rotatably mounted in the bore and having a main key slot and a change key slot formed therein and extending in a longitudinal direction with respect to said cylindrical bore; drivers movably mounted in the body for radial movement relative to the bore, and for movement partially into the bore; tumbler assemblies movably mounted in the plug for radial movement relative to the bore and movable to a position projecting from the plug, the tumbler assemblies and drivers contacting each other in one position of said plug in relation to said body, each of said tumbler assemblies comprising: a cap positioned for contacting one of said drivers when said plug is in said one position; a plunger movably mounted relative to said cap for adjusting the length of the tumbler assembly, and having a portion projecting into said main key slot; a locking pin engaging said plunger with said cap to prevent relative movement therebetween and to selectively fix the length of the tumbler assembly, a portion of said locking pin projecting into said change key slot; and cam plates each contacting one of said locking pins aNd each movably mounted in a slot in said plug and having a cam surface projecting into contact with the wall of the bore in said body, said cam plates each having said cam surface positioned for contacting one of said drivers to permit radial displacement of said locking pins and cam plates when said plug is rotated to a second position relative to said body.
 2. A lock as defined in claim 1 wherein each of said locking pins is T-shaped in configuration and includes: a barrel extending slidably through said cap; a tip on the end of said barrel and engageable with said plunger in one position of the locking pin; and a flange portion contacting one of said cam plates and spaced from said cap to permit a change key to be passed between said flange portion and said cap.
 3. A lock as defined in claim 1 wherein said plug is further characterized in having a plurality of longitudinally spaced, substantially semicircular slots extending radially inwardly therein from the outer peripheral surface thereof, and having a longitudinally extending slot extending radially therein from the outer periphery thereof and intersecting said semicircular slots at substantially a right angle, each of said semicircular slots receiving one of said cam plates.
 4. A lock as defined in claim 2 and further characterized to include locating pins extending from opposite sides of each of said plates into said longitudinally extending slot.
 5. A lock as defined in claim 1 and further characterized as including a spring contacting each of said drivers and located radially outwardly thereof for biasing said driver radially inwardly in said body toward said cylindrical bore.
 6. A lock as defined in claim 1 and further characterized as including a spring positioned between each of said caps and the associated plunger in each of said tumbler assemblies for biasing each plunger toward said main key slot, and each of said caps radially outwardly relative to said cylindrical bore.
 7. A lock as defined in claim 1 wherein each of said plungers has a plurality of circumferential ribs spaced from each other therealong and selectively engageable by one of said locking pins.
 8. A lock as defined in claim 1 wherein each of said caps is generally cylindrical in configuration and receives a portion of the associated plunger therein, each cap further having a bored side arm projecting from one side thereof and slidingly receiving a portion of one of said locking pins.
 9. A lock as defined in claim 8 wherein each of said locking pins is T-shaped in configuration and includes: a barrel extending slidably through the bored side arm of the cap associated therewith; a tip on the end of said barrel and engageable with the portion of the plunger in said cap; and a flange portion contacting the outer end of said side arm and contacting one of said cam plates, said flange portion being spaced from the cap associated therewith to permit a change key to be passed between said flange portion and said cap.
 10. A lock as defined in claim 9 wherein said plug is further characterized in having a plurality of longitudinally spaced, substantially semicircular slots extending radially inwardly therein from the outer peripheral surface thereof, and in having a longitudinally extending slot extending radially therein from the outer periphery thereof and intersecting said semicircular slots at substantially a right angle, each of said semicircular slots receiving one of said cam plates.
 11. A lock as defined in claim 10 and further characterized to include locating pins extending from opposite sides of each of said cam plates into said longitudinally extending slot.
 12. A lock as defined in claim 11 and further characterized to include springs contacting each of said drivers and located radially outwardly thereof for biasing each driver radially inwardly in said body toward said cylindrical bore.
 13. A lock as defined in claim 1 and further characterized as including a spRing positioned between each of said caps and the associated plunger in each of said tumbler assemblies for biasing each plunger toward said main key slot and each of said caps radially outwardly relative to said cylindrical bore.
 14. A lock comprising: a body having a cylindrical bore therein; a cylindrical plug rotatably mounted in the bore and having a main key slot and a change key slot formed therein; drivers movably mounted in the body for radial movement relative to the bore and for movement partially into the bore; tumbler assemblies movably mounted in the plug for radial movement relative to the bore and movable to a position projecting from the plug, the tumbler assemblies and drivers contacting each other in one position of said plug in relation to said body, each of said tumbler assemblies comprising: a first part positioned for contacting one of the drivers when said plug is in said one position; a second part movably mounted relative to said first part for adjusting the overall length of the tumbler assembly, and having a portion projecting into said main key slot for cooperation with a main key inserted therein; a locking pin engaging said second part with said first part to prevent relative movement therebetween and to selectively fix the length of the tumbler assembly, a portion of said locking pin projecting into said change key slot for cooperation with a change key; and cam means contacting each of said locking pins and each movably mounted in said plug, each of said cam means having a portion projecting into contact with the wall of the bore in said body and aligned with said drivers for contacting said drivers to permit radial displacement of the drivers in the body, and a following movement by the cam means to permit radial displacement of said locking pins and cam plates when said plug is rotated to a second position relative to said body. 